Various sensors and gauges use delay measurements of acoustic and optic pulses or coded signals. In some applications, the measurement of a distance is coupled with pattern detection. This may be the case, for example, in some time-of-flight (TOF) techniques that use visible or infra-red light. Infra-red light may be a wavelength signal of choice in many applications because of its invisibility. Infra-red light has a penetration depth on the order of ten microns or more. At this depth a space charge region cannot be easily established by means of out-diffusion of a surface doping layer. Photonic mixing devices (PMD) are also incapable of color recognition since only infra-red pulsed light is evaluated. The photocells used give a fixed spectral response and thus are not designed to work as color recognition devices.